The central Colorado volcanic field (CCVF) is a

volcanic field A volcanic field is an area of Earth's crust that is prone to localized volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters of up to 100 volcanoes ...

in Park County,

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the ...

. It is located in the southern

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...

and covered a roughly triangular area centered on the Thirtynine Mile volcanic area and extending from the Sawatch Range southeast to the northern Sangre de Christo Range and the

Wet Mountains The Wet Mountains are a small mountain range in southern Colorado, named for the amount of snow they receive in the winter as compared to the dried Great Plains to the east. They are a sub-range of the Sangre de Cristo Mountains, in the southern R ...

and northeast to the southern

Front Range The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encountered ...

south of

Denver Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...

. The area covered by the volcanic products of the eruptions included some produced by at least ten volcanic centers or

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

s. The field overlaps the San Juan volcanic field to the west. The volcanic products date from the late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

to the early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

().

Economic significance

Rocks of the CCVF host base- and

precious metal Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lu ...

deposits, including the volcanic

diatreme A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When magma rises up through a crack in Earth's crust and makes contact with a shallow body of groundwater, rapid expansion of heated wate ...

at Cripple Creek, the site of a notable

gold rush A gold rush or gold fever is a discovery of gold—sometimes accompanied by other precious metals and rare-earth minerals—that brings an onrush of miners seeking their fortune. Major gold rushes took place in the 19th century in Australia, New ...

beginning in 1890. By 1900, more than 500 mines had been established in the Cripple Creek district, and the population exceeded 35,000. Open-pit gold mining continues today. Outcrops of Wall Mountain

Tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

, one of the most widespread

extrusive Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contra ...

units of the CCVF, may be found near the town of Castle Rock, more than from the presumed eruptive source of the tuff. Locally known as Castle Rock

Rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

, the stone was quarried for

dimension stone Dimension stone is natural stone or rock that has been selected and finished (e.g., trimmed, cut, drilled, ground, or other) to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. ...

and

construction aggregate Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregate ...

beginning in 1872 and used in building projects in cities along the Front Range, including Denver and Colorado Springs. The quarries were once important to the economy of the town of Castle Rock: in 1900, the quarries produced up to 1800 rail cars of stone per year and employed up to 100 laborers. Although major operations ceased in 1906, at least one quarry operated as of 2013.

Notable geological features

_References

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Economic significance

Notable geological features

See also

_References

References